1. Field of the Invention
The present invention relates to a toner for developing a latent electrostatic image for use in an electrostatic copier, a laser printer or the like. The present invention also relates to an electrostatic photographic apparatus and a process cartridge using the toner. More particularly, the present invention relates to a toner containing hydrophobic treated mesoporous particles as an external additive as well as an electrophotographic apparatus and a process cartridge using the toner.
2. Related Background Art
In an image forming method used in an electrophotographic apparatus and an electrostatic recording apparatus, various methods are known for forming a latent image on an electrophotographic photosensitive member (hereinafter referred to also as a “photosensitive member”) and a photosensitive member such as electrostatic recording dielectric material. For example, an electrophotographic method is generally performed as follows. That is, a photosensitive member with photoconductive layers is uniformly charged so as to have a desired polarity and potential and then subjected to image pattern exposure to form an electric latent image. The latent image is developed with a toner to be visualized, and the toner image is transferred and fixed onto a transfer medium such as paper. Recent copiers, facsimile machines, printers, or electrophotographic image-forming apparatus provided with at least two functions of these have higher resolution than ever as high as, for example, 600 or 1200 dpi. Along with this, a developing method for higher resolution and higher definition is demanded.
The electrophotographic image-forming apparatus is known to generate various discharge induced products such as NOx, SOx, and ozone due to charging energy when the photosensitive member is charged. The discharge induced products adhere onto the photosensitive member to deteriorate lubricity of the surface of the photosensitive member. With an increased amount of the discharge product on the surface of the photosensitive member, the discharge induced products absorb more moisture in the air at high humidities to decrease surface electric resistance of the electrophotographic photosensitive member. Thereby, it becomes difficult to retain an electrostatic latent image on the photosensitive member, thus generating image defects such as blurring and deletion in output toner images.
If an electrophotographic image forming apparatus may be constructed so that a member coming in contact with the surface of an electrophotographic photosensitive member, for example, a cleaning member scrapes off a relatively large amount of the surface of the photosensitive member along with the discharge induced products, image defects can be prevented from occurring. However, this construction results in such a drawback that the service life of the photosensitive member is decreased.
In this case, if the photosensitive member is highly durable, the surface of the photosensitive member tends to be hardly refreshed. Even if the surface of the photosensitive member (a drum) is scraped off, no lubricating action by generated powder is expectable. However, in the case of an organic material electrostatic carrier having a lower strength than an inorganic material electrophotographic photosensitive member, electrophotographic photosensitive members having decreased surface abrasion and an increased service life has been developed through recent progress of electrophotographic photosensitive member technology. Thus, it is desirable that the accumulation of discharge induced products due to a decrease in surface abrasion should be avoided.
Accordingly, various constructions have been proposed for removing discharge induced products adhering on the surface of an electrophotographic photosensitive member while suppressing a reduction in service life of the electrophotographic photosensitive member. For example, a discharge product removing device has been proposed including a water applying unit that applies water onto the surface of the electrophotographic photosensitive member and a water removing unit that removes water from the surface of the electrophotographic photosensitive member. The discharge product removing device utilizes such a property that the discharge induced products produced on the surface of the electrophotographic photosensitive member dissolves in water, and has such an advantage that the discharge induced products can be removed relatively effectively.
However, in general, the surface of an electrophotographic photosensitive member is hydrophobic, hence when water is applied onto the surface of the electrophotographic photosensitive member, water is formed into droplets due to water repellency of the surface of the electrophotographic photosensitive member and the droplets are scattered thereon. Therefore, even if the discharge induced products are dissolved in water applied onto the surface of the electrophotographic photosensitive member, the aqueous solution containing the discharge induced products in the form of droplets adheres on the surface of the electrophotographic photosensitive member in a thinly scattered state. Since the droplets are thinly scattered on the surface of the electrophotographic photosensitive member, when wiped off, the effect of removing discharge induced products is different between portions of the surface of the electrophotographic photosensitive member where droplets are adhered and portions of the surface of the electrophotographic photosensitive member where no droplets are present, so the properties of the surface of the electrophotographic photosensitive member after the wiping may be non-uniform.
If the image forming apparatus is constructed so that the discharge induced products on the electrophotographic photosensitive member can be removed, the discharge induced products can not be sufficiently removed if the adhesion amount of the discharge induced products on the surface of the electrophotographic photosensitive member becomes large, thus it may be difficult for image defects to be reliably prevented.
Further, there has been proposed a method of supplying a compound that has an acid-receiving effect, such as hydrotalcite, to an electrophotographic photosensitive member. According to this proposal, the hydrotalcite compound is a lamellar compound that has a positively charged [Mg++2(1-x)Al+++2x(OH−1)4] layer and a negatively charged [CO3−−x.mH2O] layer. The CO3−− in the structure is ion-exchangeable and is easily replaced by another anion to adsorb acids. This action decreases the influence of the discharge induced products. However, a toner containing such an ionic compound may adversely affect electric properties of the toner, for example, before and after absorbing moisture. Further, it has been proposed that zeolite is used as a polar adsorbent composed of inorganic particles (Japanese Patent Application Laid-Open No. 2003-091223). However, in general, zeolite crystals contain cations exchangeable for water molecules in a large cavity composed of a condensed anion having a three-dimensional skeleton structure of alminosilicate. Therefore, zeolite is an ionic compound similar to the above-mentioned hydrotalcite, and may have similar drawbacks.
Zeolite, a porous material, has a pore diameter of less than 2 nm and is classified into a microporous material. When a microporous material having an original small pore diameter is surface-treated with a silane-coupling agent or the like to suppress water absorption of inorganic particles, molecules of the silane-coupling agent entering into pores occupy a large proportion of the pores and the net pore diameters after the treatment would become small. This is supposed to prevent compounds to be adsorbed from entering the pores. Therefore, a toner is sought in which a change in characteristics due to a hygroscopic property is suppressed and harmful substances are adsorbed and removed when a porous material is used as an external additive.